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Platforms and Design Aids for Low Power Mobile Computing

Platforms and Design Aids for Low Power Mobile Computing. Vijay Raghunathan ( vijay@ee.ucla.edu ) EE202A tutorial (Fall 2004) Ack: Ubiquity SRP Team, Intel Research. Taxonomy of wireless devices. Mobile computing devices (Devices / person ~ 1). Capabilities, Performance.

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Platforms and Design Aids for Low Power Mobile Computing

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  1. Platforms and Design Aids for Low Power Mobile Computing Vijay Raghunathan (vijay@ee.ucla.edu) EE202A tutorial (Fall 2004) Ack: Ubiquity SRP Team, Intel Research

  2. Taxonomy of wireless devices Mobile computing devices (Devices / person ~ 1) Capabilities, Performance Handheld personal devices (Devices / person > 1) “Embedded” ubiquitous devices (Devices / person >> 1) Size, Power Consumption, Cost

  3. Example: 3G handset • Mitsubishi D-2101V WCDMA 3G handset • Introduced in 2002 by NTT DoCoMo • 160g, Dual camera, 3x optical zoom • 54 minutes talk, 55 hour standby • 43 ICs, 775 discrete components, 14.6 cm2 • 4 different PCBs

  4. Intel’s embedded platforms Consus (SA1110) (2001) Stayton (PXA250) (2002) Stargate (PXA255) (2003)

  5. What is Stargate? • A single board wireless mobile computing platform • Leverages advances in computation, communication and storage to enable wireless systems research

  6. System architecture

  7. System software • Compaq Bootloader 2.4.15 (ported to XScale) • Initializes the board (GPIO, clocks, UART, OS timer, etc.) • Linux Kernel 2.4.19-rmk7 • Basic device drivers • Ethernet, 802.11, Bluetooth, USB, Serial (mote, console), etc. • Other software • Standard Linux utilities, secure server and clients, Java VM (Wonka), Apache web server, Darwin streaming media server • SW and manuals can be downloaded from Sourceforge site • http://platformx.sourceforge.net

  8. Computation subsystem • PXA255 based on XScale micro-architecture • Successor to the StrongARM family • 2.3 nJ/instruction at 200 MHz, 1.5V • Several sleep modes, rich set of peripherals

  9. Communication: Bluetooth • 2.4 GHz band, FHSS, Master-Slave arch., 0 to 20 dBM • Zeevo single chip Bluetooth module • ARM7TDMI, 64KB SRAM, 512KB FLASH, USB, UART • Remote wakeup feature • Event driven power management (~10mW) • BlueZ open source Linux drivers from Qualcom

  10. Communication: IEEE 802.11 • Through the PCMCIA or Compact Flash slot • HostAP Linux driver • Support for infrastructure or ad-hoc mode • Wireless extensions API and tools • 1.2W in transmit mode, 1W in receive mode

  11. Mote interface • 51 pin mote connector • Communication using UART, GPIO lines • Stargate acts as a sensor network gateway • Mote can be re-programmed by PXA255 … struct termios newtio; … input_stream = open(SERIAL_DEVICE, O_RDWR|O_NOCTTY); … count = read(input_stream, input_buffer, 1)

  12. Dynamic voltage scaling • PXA255 can operate at either 100, 200, 300, or 400 MHz • Provides super-linear savings in dynamic power (V2 * f) • Leakage reduces the effectiveness of DVS • echo 1 > /proc/dvfs/dvs_enable • echo X > /proc/dvfs/dvfs_mode • Gas gauge to read core voltage, battery voltage and current

  13. Mote based wakeup • XScale processor can be shut down to save power • Mote can wakeup the processor through GPIO pins • Provides scalable computation on the node void wakeupPS( ) { //Generate a pulse on PORTB, pins 5 and 4 //connected to the GPIO1 and GPIO2 of the //PXA255. uint8_t regstatus; regstatus = inp(PORTB); outp(0x30, DDRB); regstatus |= 0x30; //sets bits 5 and 4 outp(regstatus, PORTB); regstatus &= ~0x30; //clears bits 5 and 4 outp(regstatus, PORTB); }

  14. Mote Bluetooth IEEE 802.11 Hierarchical radios • Supports three radios with different power/performance • Combined to form heterogeneous communication subsystem • Hierarchical device discovery and connection setup scheme leads to up to 40X savings in discovery power Idle current Startup time Energy per bit

  15. Power measurement setup • NetDAQ data acquisition system from Fluke • Small series resistor along power supply path • 1000 samples per second, high precision • 20 channels for monitoring individual system components Page Inquiry

  16. Active mode power split up

  17. PXA255 Radio subsystem Shutdown and power gating • Wireless cards are often inefficient at shutdown • Low-level firmware, device drivers, vendor specific design • Power gating decreases this to 1mW

  18. Impact of flash writes • Flash writes determine application throughput • Higher bandwidth capability of 802.11 is wasted

  19. Application characteristics • Bluetooth is often sufficient for streaming media • 802.11 causes power penalty for unused performance

  20. The Personal Server concept Wireless disk drive Working data set cache No display / keyboard Use local computing infrastructure to interact with “your own data”

  21. Other applications • Seismic monitoring, personal exploration rover, mobile micro-servers, networked info-mechanical systems, hierarchical wireless sensor networks [NESL, UCLA] [Robotics, CMU] [NIMS, UCLA] [CENS, UCLA] [Intel + UCLA]

  22. Gumstix • Lightweight PXA255 based platform (weighs 8g) • 64MB SDRAM, 4MB Flash, Bluetooth, USB, MMC/SD • Linux kernel version 2.6 • Draws ~250mA at 400 MHz without Bluetooth • USB based TCP/IP networking

  23. B#: Battery emulator • Intelligent power supply that mimics battery behavior • Can profile, simulate, or emulate batteries • Several inbuilt battery models (Li-ion, coin cell, etc.)

  24. B#: Battery emulator

  25. References • Stargate SW website: http://platformx.sourceforge.net • Intel PXA255 processors http://www.intel.com/design/pca/prodbref/252780.htm • V. Raghunathan, et al., “Experience with a low power wireless mobile computing platform”, Proc. ACM ISLPED, 2004 http://www.ee.ucla.edu/~vijay/files/islped04_consus.pdf • Gumstix, http://www.gumstix.com • P. Chou, et al., “B#: A battery emulator and power profiling instrument”, Proc. ACM ISLPED, 2003. http://newport.eecs.uci.edu/bsharp/

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